Method for producing a high-quality insulation of electric conductors or conductor bundles of rotating electrical machines by means of spray sintering

ABSTRACT

The present invention discloses a process for producing a high-quality insulation for conductors or conductor bundles of electrical machines by means of spray-sintering. Unlike in the prior art, it is possible to apply internal corona-discharge protection, insulation and external corona-discharge protection to conductors or conductor bundles in which, on account of a very low level of defects in the insulation and its inherent resistance to partial discharges, it is possible to dispense with the use of winding processes using glass/mica tapes. This eliminates the need to use complex special equipment and allows the throughput times to be shortened considerably.

TECHNICAL FIELD

The invention relates to the field of the insulation of rotatingelectrical machines. In particular, the invention relates to a processfor producing a high-quality insulation for conductors or conductorbundles as are used in rotating machines, for example in the form ofstator coils, transposed bars and excitation conductors.

PRIOR ART

Various processes are customarily used in the field of the insulation ofconductors or conductor bundles of rotating electrical machines.

In one process, tapes comprising a glass-fiber support and mica paperare wound helically in layers onto a stator conductor until a desiredinsulation thickness is reached. Subsequent impregnation in epoxy resindisplaces residual air from the insulating winding formed in this way,and the layers of tape are adhesively bonded. Curing in a suitable moldimparts the final shape to the insulation. For production reasons, inthis process the mica platelets are oriented in the direction of thetape, which in the finished insulation results in the mica plateletsbeing oriented parallel to the conductor surface. In the resin richtechnique, epoxy resin in the B state is admixed with the tape and isconsolidated by hot pressing of the bar.

According to a further process, which is known from EP 0 660 336 A2,tapes consisting of thermoplastic filled with mica are wound around thestator conductor. Consolidation and shaping in this case take place bymeans of hot pressing of the stator conductor around which the tape hasbeen wound, during which process air is displaced, the thermoplastic ismelted and the layers of the winding are adhesively bonded. In thisprocess too, the mica platelets are oriented parallel to the conductorsurface. However, the air is not completely expelled in any of theprocesses. Air-filled gaps and holes remain, in which, in the event of avoltage load, partial discharges in the nC range and above occur.

Finally, the stator conductor can also be insulated by extrusion ofthermoplastics without fillers, i.e. also without mica, as described inU.S. Pat. No. 5,650,031.

Nowadays, however, the conductors of rotating electrical machines whichare to be insulated are generally structures of a very complex shape, inthe form of bars or coils. A straight part of the conductors is locatedin the grooves of the stator of the machine. A curved part of theconductors, after suitable connection to adjacent bars and coils, formsa winding head which projects out of the stator at both ends. In thecase of large rotating machines, the length of the straight part mayexceed 6 m. A problem hitherto has been that insulation and conductorusually have different coefficients of thermal expansion α which, overthe course of time, on account of thermal stresses, may lead to defectsin the insulation as a result of cavities which form where theinsulation becomes detached, and that defects, for example inclusions ofair, are formed during the production of the insulation. Partialdischarges may occur at such defects, leading to damage to theinsulation. In this case too, partial discharge activities in the 100 nCrange are quite customary.

In view of these partial discharge activities, hitherto it has only beenpossible for the machine insulation to operate reliably as a result ofthe barrier action of mica platelets oriented perpendicular to the fielddirection. This prevents the formation of flashover passages leading outof the cavities. 2.5 to 2.75 kV/mm is generally regarded as the upperlimit for long-term reliability of the operating field strength.However, a maximum level such as this is exceeded, in some casesconsiderably, by other insulation systems used in medium- orhigh-voltage insulation.

For example, the maximum field for long-term operation in pin-typeinsulators, in which an alumina-filled epoxy resin is used forgas-insulated circuits, is 4 kV/mm, and the maximum field forhigh-voltage cables, in which polyethylene is used, is approx. 12 kV/mm.A common feature of these conventional insulation systems is that thereare no partial discharges under operating load.

However, since, moreover, the conventional processes and materials usingmica which are currently in use are substantially already more thanthirty years old, at best incremental improvements are to be expectedfrom any further developments to this prior art. Therefore, it appearshighly unlikely that it will be possible to further develop this priorart to develop a higher-quality insulation which can be produced withshorter throughput times and lower manufacturing costs compared to theprior art, and also in an environmentally friendly production process,i.e. without the use of solvents, without emissions and without theproduction of special waste, and which does not include any defects or,if there are defects, these defects do not lead to any partialdischarges.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide a processfor producing a high-quality insulation for conductors or conductorbundles in which the insulation has a high quality and can be producedwith short throughput times, low manufacturing costs and in anenvironmentally friendly manner.

One aspect of the present invention includes a process for producing ahigh-quality insulation of conductors or conductor bundles.

This inventive process for producing a high-quality insulation forconductors or conductor bundles without cavities which may lead topartial discharges under test and operating loads means that theoriented mica platelets are no longer required. This greatly facilitatesboth the choice of production processes and the choice of materials forthe insulation, since for many polymers it is difficult to incorporatemica in concentrations of more than 40% by weight.

BRIEF DESCRIPTION OF THE DRAWING

The invention is explained in more detail below with reference to apreferred exemplary embodiment which is illustrated in the drawing andin which:

FIG. 1 shows a structure of the spray-sintering device according to theinvention, and

FIG. 2 (FIG. 2-1 and FIG. 2-2) shows a flow diagram which illustratesthe way in which the process according to the invention is carried out.

EXEMPLARY EMBODIMENTS OF THE INVENTION

The following text provides an extensive description of a process forproducing a high-quality insulation for conductors or conductor bundlesof, for example, rotating electrical machines. First of all, the basicstructure of the insulation will be dealt with, and then the processaccording to the invention will be explained in detail.

The insulation which is applied using the process according to theinvention comprises three layers. The first layer forms an internalcorona-discharge protection, consisting of conductively orsemiconductively filled polymer. In this case, a polymer which can besuccessfully joined to the polymer material of the insulating layerwhich follows it is used. It is preferable to use the same polymer as inthe insulating layer.

As is the case in high-voltage cables, the internal corona-dischargeprotection has the role of decoupling electrical and mechanical boundarylayers. In electrical terms, the internal corona-discharge protectionhas the same potential as the metallic conductor below it, i.e. is partof the electrical conductor; in mechanical terms, by contrast, it ispart of the insulation. This ensures that any points where theinsulating sleeve and conductor become detached are free from partialdischarges, since there is no voltage drop across the detachment.

The process according to the invention for the production of thishigh-quality insulation for conductors or conductor bundles is intendedto satisfy the following demands:

-   -   1) The production process is to be substantially independent of        the particular geometry of the initial bar or coil, i.e. of the        transposed, uninsulated, consolidated bar or coil.    -   2) The insulation is to be of a high quality, i.e. compared to        the prior art is to have an improved thermal stability up to        approx. T_(max)=180° C. and is to be able to withstand long-term        operation at approx. 5 kV/mm on the flat sides of the conductors        without being damaged.    -   3) Furthermore, the process is to allow production of an        insulation of constant thickness with a tolerance Δd/d<10%—even        if the tolerances of the initial bar or coil are considerably        greater—while it is to be possible to produce layer thicknesses        of from 0.3 to 7 mm.    -   4) To shorten the production time, the throughput time per bar        or coil is to be at most 1 to 2 hours.

In view of these demands which are to be satisfied by the processaccording to the invention, one could consider using conventionalspray-sintering processes as the starting point.

A conventional spray-sintering process of this type is described, forexample, in German patent DE 39 36 431, entitled “Process for applying alayer of plastic to a metallic conductor”. In this conventional process,to apply a layer of plastic to a metallic conductor plastic powder iselectrostatically charged, is deposited on the preheated metallicconductor and is then melted. The process is used to producesubconductor insulations, i.e. insulations with a low voltage load. Thisconventional spray-sintering process would require a significantly loweroutlay on manufacturing technology than the conventional insulatingprocess which involves winding a wide range of tapes around theconductor. This would make it possible to eliminate the use of expensivespecial equipment, such as for example winding robots, vacuum/pressurevessels, devices for the cooled storage of liquid resin. They would bereplaced by commercially available coating units and commerciallyavailable robots.

It would also be possible for this conventional spray-sintering processto be automated to a far greater extent than the conventional process.The throughput times would be only 0.5 to 3 hours, instead of severaldays. The saving on investment costs would lead to the possibility ofachieving both shorter throughput times and lower production costs.

However, it has proven to be a problem that the technique ofspray-sintering or electrostatic spraying is currently generally onlyused for the dry painting of a very wide range of components, forexample refrigerators, automobiles, garden furniture, etc., with verylow layer thicknesses of approx. 80 μm. In the field of electricalengineering, this technique has hitherto only been used for theinsulation of busbars in the medium- and high-voltage range. As hasalready been mentioned above, however, the insulation described above isonly used to insulate subconductors in which there are only lowpotential differences.

In this conventional application in the field of insulation for busbars,however, unlike the high-quality insulation which is to be produced bythe process according to the invention there is only a weak electricalload on the insulation, since the ground electrode is absent on theinsulation, and therefore the voltage is for the most part reduced viathe ambient air. Since, therefore, the electrical load is considerablylower, in the prior art the demands with regard to insulation thicknessand freedom from defects are considerably lower than for the processaccording to the invention, and therefore defects are acceptable sincethere is no risk of partial discharges. It is customary to use a powderwhich is based on epoxy resin, but in the current composition thispowder cannot be used at above T=130°, on account of high dielectriclosses. Moreover, sample coatings using this powder have high levels ofpores.

Therefore, compared to the known prior art of spray-sintering, theprocess according to the invention for the production of a high-qualityinsulation for conductors or conductor bundles requires numerousmodifications in order to solve problems which have not hitherto beentaken into account and to eliminate properties which are advantageousfor this process in its conventional application but cause problems witha view to achieving the objectives of the invention.

FIG. 1 diagrammatically depicts a device for carrying out the processaccording to the invention; for the sake of simplicity, some elementsare not shown in FIG. 1 but rather are merely described in detail.

The central appliance for carrying out the process according to theinvention is a spray gun 1. Coating material 2 in powder form, forexample thermally crosslinking epoxy powder, is fed in fluidized form tothis spray gun 1 from a reservoir 6. The fluidizing medium is in thiscase preferably dried air or nitrogen. The spray gun 1 may have a device3 for electrostatically, i.e. negatively, or tribo-electrically, i.e.positively, charging the coating material 2, i.e. the powder particles.

However, it is not absolutely imperative for the coating material 2 tobe electrically charged in the process according to the invention.Nevertheless, this charging has the advantage that greater amounts ofmaterial are applied at points and edges of a conductor which is to beinsulated, on account of the local increase in the electric field. Thiscan be influenced by adjusting the high voltage at the device 3. This isoften desirable, since at these points the field strength is also higherin operation, and experience has shown that this is where voltage tendsto break through the insulation.

In the process according to the invention, the spray gun 1 is moved pasta heated substrate 4 which is to be coated, for example a conductorwhich is to be coated, at a constant distance, for example approx. 100to 300 mm, a constant speed, for example approx. 50 to 800 mm/s, andwith a constant delivery of powder, for example approx. 30 to 250 g/min.The spray gun 1 is preferably guided by means of an automaticdisplacement unit, e.g. a robot. The substrate is heated throughout theentire coating process. Since the present example relates to anelectrical conductor, this can easily be achieved by electrical heating.Specifically, the substrate 4 can be heated either by resistance heatingby means of direct current or low frequency, for example at 50 Hz, or byinductive heating by means of medium frequency or high frequency. Forthis purpose, by way of example a current source 5 is provided. Thetemperature of the substrate surface 4 a which is to be coated isselected in such a way that the coating material 2, for example theepoxy powder, melts when it comes into contact with the surface and isthen thermally crosslinked, i.e. cured.

In addition to the heating during coating which is described here, it isalso conceivable to use methods in which the object to be coated ispreheated (for example in a separate furnace), and is then transferredto the coating installation. On account of the high heat capacity ofcopper, it is now possible for the bar or coil to be coated with atleast part of the total insulation thickness required. If the surfacetemperature drops to such an extent that the powder no longer melts toform a smooth film, but rather adheres in the form of a sand-likecovering, it is necessary to supply further heat. The question ofwhether heating takes place continuously during coating or heating andcoating cycles alternate makes no difference to the quality of thefinished insulation. It is sensible to use the intermediate heating in afurnace if, in the case of objects with a very large Cu cross section,resistive heating or inductive heating are difficult to implement (onaccount of difficulties with introducing the current and contactresistance, or because HF sources in the 15 to 10 kA range are expensiveand have to be shielded at high cost, respectively).

In an advantageous embodiment, the “furnace” comprises an assembly of IRradiators which is drawn or moved or fitted over the object mounted onthe coating installation.

In the process according to the invention, the coating takes place inlayers until the desired thickness of the insulation is reached, unlikein the prior art, in which the coating takes place in a single path. Inthis process, one layer corresponds to the insulating layer which isproduced by means of one spray pass. In this case, after a spray pass,the coating material must be given sufficient time to melt, run andcrosslink sufficiently for it no longer to be able to flow. Therefore,the gel time, which is to be explained in more detail below, is ofconsiderable importance.

In principle, it is generally possible to build up layers with athickness of 1 mm and more in one spray pass. However, tests have shownthat for layer thicknesses of greater than 0.2 mm the number of bubbles,i.e. defects, in the insulation rises considerably, but hitherto thesebubbles have not presented any problems in the application area ofspray-sintering. The reason for the formation of bubbles at layerthicknesses of >0.2 mm is that adsorbed substances and impurities with alow vapor pressure are no longer able to evaporate out freely at highlayer thicknesses. In conventional applications, this formation ofbubbles caused few problems, but it does represent a drawback for theinsulation according to the invention, and this drawback is to beavoided by the process according to the invention. Therefore, in theprocess according to the invention the insulation is applied insuccessive steps, in layer thicknesses of up to 0.2 mm, so that thedesired freedom from defects can be achieved.

The constant spraying distance, spray-gun speed of movement and deliveryof coating material and powder as explained above results in a thicknessconsistency of better than 0.08 mm for total thicknesses of approx. 1mm. Since the rate can be changed very easily and in a very controlledway, the process according to the invention is able to locally vary thethickness of the insulation. For example, it is possible to increase theinsulation thickness on the narrow sides of the transposed bar comparedto the thicknesses on the wide sides, with the result that theelectrical field strength is reduced without the groove width having tobe increased or without the dissipation of heat from the bar, whichtakes place via the wide sides, being impeded.

Furthermore, with the process according to the invention it is alsopossible to reduce the insulating thickness in the bow region oftransposed bars, where the electric field load is generally lower thanin the straight part. An axial variation in the thickness or compositionof conductive or semiconducting layers also leads to possibilities withregard to field dissipation which cannot be achieved or can only beachieved with difficulty using the conventional system.

If the thickness tolerance referred to above is insufficient or if acomplicated layer distribution is desired, it is additionally possibleto adapt the rate of movement of the spray gun, by contactlessmeasurement of the current layer thickness at a given location x, y, zby means of infrared and by suitable feedback to the control system ofthe robot, in such a manner that the final thickness at the location x,y, z corresponds to the desired value.

In principle, all thermally crosslinkable plastics, known as thermosets,can be used as materials for the insulation. The requirement that theinsulation be thermally suitable for use at up to 180° C. in the presentapplication is best satisfied by epoxy materials. These materialsconsist of a mixture of at least one uncrosslinked resin and at leastone hardener (as well as a few further additions, such as accelerators,pigments, etc.) and inorganic fillers. The mixture is solid up to atleast 50° C. The melting and curing temperatures and the glasstransition temperature T_(g) vary according to the chemical compositionof resin and hardener. The temperature profile of the mechanical anddielectric strength is closely linked to the glass transitiontemperature T_(g). If it is desired for the insulation to be usable forthermal class H, T_(g) should lie in this range, preferably between 150°C. and 200° C. Glass transition temperatures of significantly above 200°C. are, on the one hand, difficult to achieve and, on the other hand,lead to a material which is relatively brittle in the region of roomtemperature.

The abovementioned, desired freedom from bubbles is dependent not onlyon process parameters, such as the application thickness, but also onmaterials properties.

It is important that the epoxy in the liquid state has a sufficientlylow viscosity to run and for the gel time to be long enough for all thebubble-forming impurities to have evaporated. This requirement for longgel times contradicts the conventional trend in powder coating where thespray-sintering technique has hitherto been used, namely that ofdeliberately establishing short gel times, for example typically of 15s, by the addition of accelerators in order to achieve high throughputtimes during thin-film coating. However, by reducing the level ofaccelerator, it is possible without difficulty to achieve gel times forcommercially available powders of ≧40 s, which is sufficiently long forthe present application.

For spray powders, the viscosity is generally not measured and specifiedas a separate variable; rather, what is known as the run, resulting fromthe viscosity and gel time, is specified. Bubble-free layers areachieved if the run is >30 mm.

Filling with inorganic fillers is in principle desirable in order toreduce the price, improve the creep strength, reduce the coefficient ofthermal expansion and improve the thermal conductivity of theinsulation. The proportion of filler in the total mixture should amountto 5–50% by weight, based on a closed filler density of up to 4 g/cm³.Examples of conventional fillers are silica flour, wollastonite, talcand chalk dust with grain sizes of around 10 μm (mean grain size d₅₀).To produce a spray powder, the filler is mixed and compounded withresin, hardener and further additives. The compounded product is thenmilled to form powder.

These milling processes are usually carried out in appliances made fromsteel or hard metal (Mohs hardness 5–6). The use of hard fillers, e.g.silica flour (hardness 7), leads to metallic abrasion, preferably in theform of chips in the sub-mm range. These are incorporated in theinsulation and, on account of their acicular geometry, lead to locationswhere the electric field strength is locally very greatly increased,where experience has shown that an electrical breakdown can occur. Theabrasion is avoided by using “soft” fillers (Mohs hardness≦4), e.g.chalk dust, and/or by using relatively fine fillers with d₅₀<<1 μm, e.g.clay, SiO₂, ZnO or TiO₂.

Furthermore, fine fillers of this type have the advantage that, even ifdefects such as cavities or metallic inclusions are present, theyprevent or at least very considerably delay electrical breakthroughs, asdisclosed, for example, in U.S. Pat. No. 4,760,296, in the name ofJohnston et al., or in German patent application DE 4037 972 A1. Inthese two publications, the effect of increasing the service life isachieved by completely or partially replacing the coarse filler withfillers which have grain sizes in the nanometer range (0.005 to 0.1 μmmaximum grain size). However, nano fillers have the unacceptableadditional property of greatly increasing the melt viscosity of thepowder mixture, known as the thixotropy effect. This causes problemsboth during production of the powder and during processing thereof.Nevertheless, nano fillers represent a usable alternative for increasingthe service life. However, for the application according to theinvention it has also been found that the alternative of using TiO₂powder with mean grain sizes of approx. 0.2 μm to completely orpartially replace coarse fillers does not lead to a disadvantageousincrease in the melt viscosity yet nevertheless does produce the effectsof increasing service life in the same way as nano fillers. Theproportion of TiO₂ powder in the total mixture should be at least 3%,preferably at least 5%.

Conductive layers which are used for internal corona-dischargeprotection and external corona-discharge protection can be produced bythe use of conductive fillers, such as for example graphite, carbonblack and/or metal powder.

The process sequence involved in the novel insulation of electricalconductors in accordance with the invention will now be described belowon the basis of the fundamental explanations of the materials and of thedevice which have been presented above.

The process comprises the following steps:

1) Mounting the Coil or Bar which is to be Coated on a Rotation Device

In a first step S1, a bar or coil which is to be coated is mounted on arotation device. In this case, the bar ends or coil eyelets are theholding points. The bar or coil is advantageously prestrengthened byinternal adhesive bonding of the conductors or by winding a tape aroundthem, since this facilitates handling, but this is not an imperativecondition. In the case of relatively large objects, intermediatesupports are useful in order to ensure reliable securing on the rotationdevice and accurate positioning. The rotation device with the coil orbar mounted on it is actuated by means of a control device, which isadvantageously included in the control unit of a spray device.

2) Heating of the Bar or Coil

In the second step S2, the bar or coil is connected to electricalheating. This electrical heating may, for example, be resistance heatingproduced by direct current or low frequency, e.g. 50 Hz, or inductiveheating by means of medium frequency or high frequency. This heating isused to heat the bar or coil to a desired substrate temperature.

3) Orienting the Bar or Coil Position with Respect to the Spray Gun

In the following third step S3, the bar or coil position is oriented inorder for the spraying to start. During this step, one of the flat sidesof the bar or coil is oriented perpendicular to the spray gun.

4) Spraying an Internal Corona-Discharge Protection onto the Bar or Coil

There then follows, as the fourth step S4 and therefore the first actualcoating step, spraying of an internal corona-discharge protection inhorizontal paths. The movement of the spray gun takes place in such amanner that a homogeneous layer thickness profile is produced. For thispurpose, it may be necessary, in the case of very wide bars, to spray aplurality of overlapping paths in parallel. In this case, a conductiveor semiconducting thermoset is used as the coating powder which issprayed on. To accelerate the spraying, in the case of large objects itis possible to use a plurality of spray guns at the same time. Theintermediate supports used to stabilize the position of relatively largeobjects move away automatically when the spray gun approaches, in orderto allow complete coating of the bar or coil. It is easy to vary thelayer thickness applied to the bar or coil by means of the quantity ofcoating powder which is delivered and the rate of movement of the spraygun. The layer thickness is generally≦0.2 mm per pass, in order toensure that the layer is in each case free from bubbles.

5) Rotation of the Bar or Coil and Repetition of Steps S3 and S4

As the following fifth step S5, after the coating of a flat side hasended, the bar or coil is rotated, so that a further, as yet uncoatedbar or coil side faces the spray gun. Then, the third and fourth stepsS3 and S4 are repeated in order to coat the next side of the bar orcoil. In the same way, the fifth, third and fourth steps S3, S4 and S5are repeated again for all further sides of the bar or coil, until thebar or coil has been completely coated. Moreover, in the case of coilsthe steps are repeated for the other limb of the coil.

In general, the thickness required for the internal corona-dischargeprotection is applied in a single pass; in exceptional cases, however,it is also possible to carry out a plurality of coating passes, if alayer thickness of greater than 0.2 mm is desired.

6) Curing of the Internal Corona-Discharge Protection

Then, as step 6, this internal corona-discharge protective layer iscured partially or completely, i.e. for a time of between 2 and 10 minor 20 and 60 min at 200° C.

7) Application of the Insulating Layer in Accordance with Steps S3 to S6

Then, in a seventh step S7, the actual insulating layer is applied. Inthis case, a different coating powder from the internal corona-dischargeprotection is used, specifically an insulant-filled or unfilledthermoset.

Once again, the third, fourth and fifth steps described above, unlikethe steps described above, are carried out only with the insulatingcoating powder, with layers of <0.2 mm being applied repeatedly until adesired insulation thickness is reached. In this case, after each layerhas been sprayed on, intermediate curing, which lasts from 2 to 10 timesthe gel time of the powder, is carried out. In addition, to ensure thatthe coating powder is melted on reliably, it is necessary to takeaccount of the fact that the substrate temperature may have to bereadjusted as the layer thickness increases. This is preferably carriedout without contact, for example by means of an IR pyrometer. To preventthe conductor elements and their insulation from being overheated, it ispossible to monitor the temperature-dependent resistance of theconductor.

8) Application of the External Corona-Discharge Protection in Accordancewith Steps S3, S4, S5 and S6

As the next step, which follows the application of the insulating layer(step S7), an external corona-discharge protection comprising conductiveepoxy is applied to the insulating layer. The material used and theprocess steps correspond to those described in the third, fourth andfifth steps.

9) Post-Curing of the Insulation Applied

The final step after the coating operations (steps S1 to S8) have endedis either post-curing of the insulation which has been applied usingcurrent heating on the holding device or in the furnace after removalfrom the rotation device.

Since, in this insulation process according to the invention, the barsare held at their ends, these ends are not coated. However, this doesnot have any disadvantages, since the bar ends in any case remain clearin order for circular connectors to be soldered on.

In the case of coils, on the other hand, the region of the coil eyeletis intentionally not coated. This is because this ensures thedeformability of the coils which is required for installation. The coileyelets are in this case only insulated in the installed state afterinstallation.

The following processes are recommended for this operation of insulatingthe coil eyelets:

-   -   1) Either the motor stator is positioned vertically and the        coils are heated electrically. In this case, the coil eyelets of        the lower coil end are coated with thermoset powder as a result        of the coil ends being immersed in a fluidized-bed sintering        tank. In this case, the stator is rotated through 180° and the        coil eyelets of the other stator end are coated in the same way        as that described above. This process is suitable in particular        for coating relatively small stators.    -   2) Alternatively, the motor winding is heated resistively and        the end parts of the coils are insulated by spray-sintering.        This process is advantageously used for relatively large motors,        in which the total weight of the stator is high and vertical        mounting may cause problems. Also, in the case of large machines        the distances between the coils are generally greater, and        consequently coating with a spray gun becomes easier.

In an alternative embodiment of the process according to the invention,it is possible to dispense with the step of spraying on an internalcorona-discharge protection as described in the above steps 3) to 5) ifa tape, which is provided with a conductive or semiconducting layer andtherefore forms an internal corona-discharge protection at the time ofthe prestrengthening, is used for the prestrengthening of the coil orbar.

To summarize, the invention discloses a process for producing ahigh-quality insulation for conductors or conductor bundles ofelectrical machines by means of spray-sintering. Unlike in the priorart, it is possible to apply internal corona-discharge protection,insulation and external corona-discharge protection to conductors orconductor bundles in which, on account of the absence of defects, nopartial discharges occur, without the need for complex special equipmentwhich is required for the insulation with mica which has previously beenemployed.

Therefore, the invention provides a simple, inexpensive process forinsulating conductor bars or coils with a high-quality insulation whichis free of defects and therefore free of partial discharges.

To summarize, the present invention discloses a process for producing ahigh-quality insulation for conductors or conductor bundles ofelectrical machines by means of spray-sintering. Unlike in the priorart, it is possible to apply internal corona-discharge protection,insulation and external corona-discharge protection to conductors orconductor bundles in which, on account of the very low level of defectsin the insulation and the inherent resistance thereof to partialdischarges, it is possible to dispense with the use of winding processesusing glass/mica tapes. This eliminates the use of complex specialequipment and the throughput times can be shortened considerably.

1. A process for producing an insulation for conductors or conductorbundles, the method comprising: (S1) mounting a conductor or conductorbundle which is to be coated on a rotation and holding device, theconductor or conductor bundle including flat sides; (S2) heating theconductor or conductor bundle to a predetermined substrate temperature;(S3) orienting the conductor or conductor bundle position with respectto a spray device so that one of the flat sides faces the spray device;(S4) spraying an internal corona-discharge protection layer onto theconductor or conductor bundle with the spray device; (S5) rotating theconductor or conductor bundle so that another flat side faces the spraydevice, and repeating steps S3 to S4 until all the flat sides of theconductor or conductor bundle have been coated; (S6) partially orcompletely curing the internal corona-discharge protection which hasbeen applied; (S7) applying an insulating layer in accordance with stepsS3 to S6 to all sides of the conductor or conductor bundle, with layerthicknesses of less than 0.2 mm, and curing after applying each layer;(S8) applying an external corona-discharge protection layer inaccordance with steps S3 to S6; and (S9) curing the layers which havebeen applied.
 2. The process as claimed in claimed in claim 1, whereinthe conductor or conductor bundle comprises a transposed bar or a coil.3. The process as claimed in claim 1, further comprising: (S0)prestrengthening the conductor or conductor bundle by internal adhesivebonding or by winding a tape around the conductor or conductor bundle.4. The process as claimed in claim 2, wherein the conductor or conductorbundle comprises a bar having bar ends or a coil having coil eyelets,and wherein step S1 comprises holding the bar at the bar ends or thecoil at the coil eyelets.
 5. The process as claimed in claim 1, whereinstep S1 mounting comprises holding using additional intermediatesupports in order to ensure accurate positioning.
 6. The process asclaimed in claim 1, wherein step S2 heating comprises heating theconductor or the conductor bundle by resistance heating using direct orlow frequency current, or by medium frequency or high frequencyinductive heating.
 7. The process as claimed in claim 1, wherein step S2heating the conductor or conductor bundle is performed either before orafter step S1 mounting on the rotation and holding device, whereinheating comprises heating by irradiation, and optionally furthercomprising additional heating when the substrate temperature drops belowa predetermined substrate temperature.
 8. The process as claimed inclaim 1, in which steps S4, S7 and S8, for a wide conductor or conductorbundle, comprise spraying in a plurality of parallel paths using aplurality of spray devices.
 9. The process as claimed in claim 1,wherein step S4 spraying comprises spraying a conductively orsemiconductively filled, thermally crosslinking plastic coating powder.10. The process as claimed in claim 5, wherein step S4 sprayingcomprises moving the intermediate supports away when the spray deviceapproaches.
 11. The process as claimed in claim 1, further comprising:varying a layer thickness by controlling a delivery quantity of acoating powder and a rate of movement of the spray device.
 12. Theprocess as claimed in claim 2, wherein the conductor or conductor bundlecomprises a coil, and step S5 repeating comprises repeating for anotherside of the coil.
 13. The process as claimed in claim 1, wherein step S7applying an insulating layer comprises applying an insulant-filled,thermally crosslinking plastic coating powder.
 14. The process asclaimed in claim 1, wherein step S8 applying an externalcorona-discharge protection layer comprises applying a conductive,thermally crosslinking plastic coating powder.
 15. The process asclaimed in claim 1, wherein step S9 curing comprises: curing withcurrent heating, subsequently cooling the conductor or conductor bundle,and removing the conductor or conductor bundle from the rotation device;or immediately removing the conductor or conductor bundle from therotation device, and curing in a furnace.
 16. The process as claimed inclaim 1, wherein step S4 spraying comprises charging a coating materialbefore spraying on the conductor or conductor bundle surface, saidcharging comprising electrostatic or triboelectric charging.
 17. Theprocess as claimed in claim 1, wherein steps S3 to S8 are performed toapply different layer thicknesses different conductor or conductorbundle sides.
 18. The process as claimed in claim 2, wherein theconductor or conductor bundle comprises a coil having coil sides andcoil eyelets, and further comprising (S10) after installation of thecoil, positioning a motor stator vertically, electrically heating thecoil, and immersing the coil eyelets in a fluidized bed sintering tankfor coating with epoxy, for both coil sides; or wherein the conductor orconductor bundle comprises a bar having bar ends, and further comprising(S10) resistively heating a motor winding and insulating the bar ends byspray-sintering.
 19. The process as claimed in claim 1, wherein step S7further comprises: monitoring the surface temperature without contact;and adjusting the substrate temperature when the surface temperaturedeviates from a predetermined surface temperature.
 20. The process asclaimed in claim 9, wherein the thermally crosslinking plastic comprisesan epoxy resin in the B state.
 21. The process as claimed in claim 1,wherein the spray device comprises a an adjustable displacement unit anda spray gun arranged on the adjustable displacement unit, and furthercomprising: moving the spray gun with the displacement unit and movingthe conductor or conductor bundle with the rotation and holding device,or moving only the spray gun with the displacement unit.
 22. The processas claimed in claim 13, wherein the thermally crosslinking plasticcomprises an epoxy resin in the B state.
 23. The process as claimed inclaim 14, wherein the thermally crosslinking plastic comprises an epoxyresin in the B state.
 24. A process for producing an insulation forconductors or conductor bundles, the method comprising: (S0) winding atape around the conductor or conductor bundle, the tape including aconductive or semiconductive layer and forming an internalcorona-discharge protection layer, the tape prestrengthening theconductor or conductor bundle: (S1) mounting a conductor or conductorbundle which is to be coated on a rotation and holding device, theconductor or conductor bundle including flat sides; (S2) heating theconductor or conductor bundle to a predetermined substrate temperature;(S7) applying an insulating layer to all sides of the conductor orconductor bundle, with layer thicknesses of less than 0.2 mm, and curingafter applying each layer, said applying performed according to steps(S7.1) to (S7.4) as follows: (S7.1) orienting the conductor or conductorbundle position with respect to a spray device so that one of the flatsides faces the spray device; (S7.2) spraying a layer onto the conductoror conductor bundle with the spray device; (S7.3) rotating the conductoror conductor bundle so that another flat side faces the spray device,and repeating steps S7.1 to S7.2 until all the flat sides of theconductor or conductor bundle have been coated; and (S7.4) partially orcompletely curing the layer which has been applied; (S8) applying anexternal corona-discharge protection layer in accordance with steps S7.1to S7.4; and (S9) curing the layers which have been applied.